From 05c508edc9d0b44e4706d3c2cf14ee12aac210d2 Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Fri, 28 Feb 2020 12:54:06 +0100 Subject: vt: selection, push sel_lock up commit e8c75a30a23c6ba63f4ef6895cbf41fd42f21aa2 upstream. sel_lock cannot nest in the console lock. Thanks to syzkaller, the kernel states firmly: > WARNING: possible circular locking dependency detected > 5.6.0-rc3-syzkaller #0 Not tainted > ------------------------------------------------------ > syz-executor.4/20336 is trying to acquire lock: > ffff8880a2e952a0 (&tty->termios_rwsem){++++}, at: tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 > > but task is already holding lock: > ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #2 (sel_lock){+.+.}: > mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118 > set_selection_kernel+0x3b8/0x18a0 drivers/tty/vt/selection.c:217 > set_selection_user+0x63/0x80 drivers/tty/vt/selection.c:181 > tioclinux+0x103/0x530 drivers/tty/vt/vt.c:3050 > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 This is ioctl(TIOCL_SETSEL). Locks held on the path: console_lock -> sel_lock > -> #1 (console_lock){+.+.}: > console_lock+0x46/0x70 kernel/printk/printk.c:2289 > con_flush_chars+0x50/0x650 drivers/tty/vt/vt.c:3223 > n_tty_write+0xeae/0x1200 drivers/tty/n_tty.c:2350 > do_tty_write drivers/tty/tty_io.c:962 [inline] > tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046 This is write(). Locks held on the path: termios_rwsem -> console_lock > -> #0 (&tty->termios_rwsem){++++}: > down_write+0x57/0x140 kernel/locking/rwsem.c:1534 > tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 > mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902 > tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465 > paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389 > tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055 > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 This is ioctl(TIOCL_PASTESEL). Locks held on the path: sel_lock -> termios_rwsem > other info that might help us debug this: > > Chain exists of: > &tty->termios_rwsem --> console_lock --> sel_lock Clearly. From the above, we have: console_lock -> sel_lock sel_lock -> termios_rwsem termios_rwsem -> console_lock Fix this by reversing the console_lock -> sel_lock dependency in ioctl(TIOCL_SETSEL). First, lock sel_lock, then console_lock. Signed-off-by: Jiri Slaby Reported-by: syzbot+26183d9746e62da329b8@syzkaller.appspotmail.com Fixes: 07e6124a1a46 ("vt: selection, close sel_buffer race") Cc: stable Link: https://lore.kernel.org/r/20200228115406.5735-2-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/selection.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) (limited to 'drivers') diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c index 1e132b71e127..9dae02ce4092 100644 --- a/drivers/tty/vt/selection.c +++ b/drivers/tty/vt/selection.c @@ -205,7 +205,6 @@ static int __set_selection(const struct tiocl_selection __user *sel, struct tty_ pe = tmp; } - mutex_lock(&sel_lock); if (sel_cons != vc_cons[fg_console].d) { clear_selection(); sel_cons = vc_cons[fg_console].d; @@ -251,10 +250,9 @@ static int __set_selection(const struct tiocl_selection __user *sel, struct tty_ break; case TIOCL_SELPOINTER: highlight_pointer(pe); - goto unlock; + return 0; default: - ret = -EINVAL; - goto unlock; + return -EINVAL; } /* remove the pointer */ @@ -276,7 +274,7 @@ static int __set_selection(const struct tiocl_selection __user *sel, struct tty_ else if (new_sel_start == sel_start) { if (new_sel_end == sel_end) /* no action required */ - goto unlock; + return 0; else if (new_sel_end > sel_end) /* extend to right */ highlight(sel_end + 2, new_sel_end); else /* contract from right */ @@ -303,8 +301,7 @@ static int __set_selection(const struct tiocl_selection __user *sel, struct tty_ if (!bp) { printk(KERN_WARNING "selection: kmalloc() failed\n"); clear_selection(); - ret = -ENOMEM; - goto unlock; + return -ENOMEM; } kfree(sel_buffer); sel_buffer = bp; @@ -329,8 +326,7 @@ static int __set_selection(const struct tiocl_selection __user *sel, struct tty_ } } sel_buffer_lth = bp - sel_buffer; -unlock: - mutex_unlock(&sel_lock); + return ret; } @@ -338,9 +334,11 @@ int set_selection(const struct tiocl_selection __user *v, struct tty_struct *tty { int ret; + mutex_lock(&sel_lock); console_lock(); ret = __set_selection(v, tty); console_unlock(); + mutex_unlock(&sel_lock); return ret; } -- cgit v1.2.3